Mixtures of chelating agents, and process for making such mixtures

ABSTRACT

The present invention is directed towards mixtures comprising (A) 90 to 99.999% by weight of racemic methyl glycine diacetic acid (MGDA) or of MGDA with predominantly the L-isomer in an enantiomeric excess of up to 9.5% or their respective mono-, di- or trialkali metal or mono-, di- or triammonium salts, and (B) in total 0.001 to 10% by weight of the diacetic acid derivative of aspartate as free acid or as mono-, di-, tri- or tetraalkali metal salt or as mono-, di-, tri- or tetraammonium salt, percentages referring to the sum from (A) and (B).

The present invention is directed towards mixtures comprising

-   (A) 90 to 99.999% by weight of racemic methyl glycine diacetic acid     (MGDA) or of MGDA with predominantly the L-isomer in an enantiomeric     excess of up to 9.5% or their respective mono-, di- or trialkali     metal or mono-, di- or triammonium salts, and -   (B) 0.001 to 10% by weight of the diacetic acid derivative of     aspartate as free acid or as mono-, di-, tri- or tetraalkali metal     salt or as mono-, di-, tri- or tetraammonium salt, percentages     referring to the sum from (A) and (B).

Chelating agents such as methyl glycine diacetic acid, hereinafter also MGDA, and their respective alkali metal salts are useful sequestrants for alkaline earth metal ions such as Ca²⁺ and Mg²⁺. For that reason, they are recommended and used for various purposes such as laundry detergents and for automatic dishwashing (ADW) formulations, in particular for so-called phosphate-free laundry detergents and phosphate-free ADW formulations. For shipping such chelating agents, in most cases either solids such as granules are being applied or aqueous solutions.

Granules and powders are useful because the amount of water shipped can be neglected but for most mixing and formulation processes an extra dissolution step is required.

Many industrial users wish to obtain chelating agents in aqueous solutions that are as highly concentrated as possible. The lower the concentration of the requested chelating agent the more water is being shipped. Said water adds to the costs of transportation, and it has to be removed later when MGDA is to be incorporated in a solid product. Although about 40% by weight solutions of racemic MGDA trisodium salt can be made and stored at room temperature, local or temporarily colder solutions may lead to precipitation of MGDA, as well as nucleating by impurities. Said precipitations may lead to incrustations in pipes and containers, and/or to impurities or inhomogeneity during formulation.

It can be tried to increase the solubility of chelating agents by adding a solubilizing agent, for example a solubility enhancing polymer or a surfactant. However, many users wish to be flexible with their own detergent formulation, and they wish to avoid polymeric or surface-active additives in the chelating agent.

Additives that may enhance the solubility of the respective chelating agents may be considered but such additives should not negatively affect the properties of the respective chelating agent. However, many additives have a negative effect, or they limit the flexibility for later formulations.

It has been additionally found that some samples of MGDA contain a lot of impurities that may limit their applicability in fields such as laundry detergents and ADW. Such impurities are sometimes attributed to disadvantageous colouring especially at a pH value below 10 and olfactory behaviour that sometimes goes with MGDA and other chelating agents, see, e.g., the comparative examples of U.S. Pat. No. 7,671,234.

WO 2012/150155 discloses the improved solubility of pure L-MGDA, compared to racemic MGDA. However, it is tedious to make MGDA and to carefully avoid any racemization. Although it is well possible to synthesize racemic MGDA and to separate off the D-isomer, such a method would result in disposing 50% of the yield or more.

WO 2015/036324 discloses MGDA with improved properties such as improved solubility in water. Such MGDA is based upon certain mixtures of enantiomers.

It was therefore the objective of the present invention to provide highly concentrated aqueous solutions of chelating agents such as MGDA that are stable at temperatures in the range from zero to 50° C., without the addition of surfactants or organic polymers. It was further an objective of the present invention to provide chelating agents that show an improved tolerance towards strong bases such as solid potassium hydroxide or solid sodium hydroxide. It was further an objective of the present invention to provide a method for manufacture of highly concentrated aqueous solutions of chelating agents such as MGDA that are stable at temperatures in the range from zero to 50° C. Neither such method nor such aqueous solution should require the use of additives that negatively affect the properties of the respective chelating agent. In particular, neither organic polymers nor salts of organic acids should be necessary to stabilize such solutions.

Accordingly, the mixtures defined at the outset have been found, hereinafter also referred to as inventive mixtures. Inventive mixtures display an enhanced solubility in water, compared to the pure racemic mixture of MGDA, and almost the same or the same or preferably an enhanced solubility in water, compared to the pure L-isomer of MGDA, but they are easier with respect to manufacture.

The components of inventive mixtures will be explained in more detail below.

Inventive mixtures comprise

-   -   (A) 90 to 99.999% by weight, preferably 95 to 99.99% and even         more preferably up to 99.8% by weight of racemic methyl glycine         diacetic acid (MGDA) or of MGDA with predominantly the L-isomer         in an enantiomeric excess of up to 9.5%, preferably up to 5%, or         their respective mono-, di- or trialkali metal or mono-, di- or         triammonium salts, and     -   (B) 0.001 to 10% by weight, preferably 0.01 to 5% by weight,         more preferably 0.1 to 5% by weight and even more preferably at         least 0.2% to 2% by weight of the diacetic acid derivative of         aspartate as free acid or as mono-, di-, tri- or tetraalkali         metal salt or as mono-, di-, tri- or tetraammonium salt,         hereinafter also referred to as “complexing agent (B)” or         “component (B)” or in brief “(B)”,

percentages referring to the sum from (A) and (B).

In a preferred embodiment, inventive mixtures comprise 90 to 99.9% by weight, preferably 95 to 99.5% by weight of racemic methyl glycine diacetic acid (MGDA) and in total 0.1 to 10% by weight, preferably 0.5 to 5% by weight of a mixture of enantiomers of aspartic acid diacetic acid or the respective mono-, di-, tri- or tetraalkali metal salts or the respective mono-, di-, tri- or tetraammonium salts.

The term ammonium salts as used in the present invention refers to salts with at least one cation that bears a nitrogen atom that is permanently or temporarily quaternized. Examples of cations that bear at least one nitrogen atom that is permanently quaternized include tetramethylammonium, tetraethylammonium, dimethyldiethyl ammonium, and n-C₁₀-C₂₀-alkyl trimethyl ammonium. Examples of cations that bear at least one nitrogen atom that is temporarily quaternized include protonated amines and ammonia, such as monomethyl ammonium, dimethyl ammonium, trimethyl ammonium, monoethyl ammonium, diethyl ammonium, triethyl ammonium, n-C₁₀-C₂₀-alkyl dimethyl ammonium 2-hydroxyethylammonium, bis(2-hydroxyethyl) ammonium, tris(2-hydroxyethyl)ammonium, N-methyl 2-hydroxyethyl ammonium, N,N-dimethyl-2-hydroxyethylammonium, and especially NH₄+.

In the context of the present invention, the term aspartate and aspartic acid may be used interchangeably.

In one embodiment of the present invention, component (A) is a mixture of L- and D-enantiomers of molecules of general formula (I) [CH₃—CH(COO)—N(CH₂—COO)₂]M_(3-x)H_(x)  (I)

wherein

-   x is in the range of from zero to 0.5, preferably from zero to 0.25, -   M is selected from ammonium, substituted or non-substituted, and     potassium and sodium and mixtures thereof, preferably sodium.

Preferred components (A) are the trialkali metal salts of MGDA such as the tripotassium salts, and even more preferred are the trisodium salts. The mixture of L- and D-isomers is either a racemic mixture or a mixture with low enantiomeric excess, for example up to 9.5%, preferably up to 5%. Most preferred is the racemic mixture.

In embodiments where component (A) comprises two or more compounds, the ee refers to the enantiomeric excess of all L-isomers present in component (A) compared to all D-isomers in component (A). For example, in cases wherein a mixture of the di- and trisodium salt of MGDA is present, the ee refers to the sum of the disodium salt and trisodium salt of L-MGDA with respect to the sum of the disodium salt and the trisodium salt of D-MGDA.

The enantiomeric excess can be determined by measuring the polarization (polarimetry) or preferably by chromatography, for example by HPLC with a chiral column, for example with one or more cyclodextrins as immobilized phase. Preferred is determination of the ee by HPLC with an immobilized optically active ammonium salt such as D-penicillamine.

Component (B) is selected from diacetic acid derivatives of aspartate as free acid or as mono-, di-, tri- or tetraalkali metal salt or as mono-, di-, tri- or tetraammonium salt. Component (B) may be present as racemic mixture or in the form of a mixture of enantiomers in which the L-enantiomer predominates, for example with an enantioneric excess in the range of from 5 to 99%, more preferably 15 to 90%.

Component (B) may be by present as free acid or respective salts, alkali metal salts being preferred. In preferred embodiments, the degree of neutralization of component (A) and component (B) is comparable.

In one embodiment of the present invention, component (B) is a mixture of L- and D-enantiomers of molecules of general formula (II) [OOH—CH₂—CH(COO)—N(CH₂—COO)₂]M_(4-x)H_(x)  (II)

wherein

-   x is in the range of from zero to 0.5, preferably from zero to 0.25, -   M is selected from ammonium, substituted or non-substituted, and     potassium and sodium and mixtures thereof, preferably sodium.

In one embodiment of the present invention, component (B) is the tetrasodium salt of aspartate diacetic acid.

In a preferred embodiment of the present invention, M in component (A) corresponds to M in component (B).

In one embodiment of the present invention, inventive mixtures may additionally comprise 0.01 to 5% by weight, referring to the sum of (A) and (B), of glutamic acid diacetic acid (GLDA) or its respective mono-, di-, tri- or or tetraalkali metal or mono-, di-, tri- or tetraammonium salt. In preferred embodiments, the degree of neutralization of component (B) and GLDA is the same or approximately the same.

In one embodiment of the present invention, inventive mixtures may contain in the range of from 0.1 to 10% by weight of one or more optically inactive impurities, at least one of the impurities being at least one of the impurities being selected from iminodiacetic acid, formic acid, glycolic acid, propionic acid, acetic acid and their respective alkali metal or mono-, di- or triammonium salts, if applicable.

In one aspect of the present invention, inventive mixtures may contain less than 0.2% by weight of nitrilotriacetic acid (NTA), preferably 0.01 to 0.1% by weight, or the respective alkali metal or ammonium salts.

In one embodiment of the present invention, inventive mixtures may additionally contain 0.1 to 3% by weight with respect to the sum of (A) and (B), of the tetraacetic acid derivative of lysine, or 0.1 to 3% by weight of the mono-acetate of proline.

In one embodiment of the present invention, inventive mixtures may contain one or more optically active impurities. Examples of optically active impurities are L-carboxymethylalanine and its respective mono- or dialkali metal salts, and optically active mono- or diamides that result from an incomplete saponification of the dinitriles, see below. A further example of an optically active impurity is the respective mono-carboxymethyl derivative of (B). Preferably, the amount of optically active impurities is in the range of from 0.01 to 1.5% by weight, referring to the inventive mixture solution. Even more preferred, the amount of optically active impurities is in the range of from 0.1 to 0.2% by weight.

In one aspect of the present invention, inventive mixtures may contain minor amounts of cations other than alkali metal or ammonium. It is thus possible that minor amounts, such as 0.01 to 5 mol-% of total inventive mixture, based on anion, bear alkali earth metal cations such as Mg²⁺ or Ca²⁺, or transition metal ions such as Fe²⁺ or Fe³⁺ cations.

Inventive mixtures display a very good solubility, especially in water and aqueous alkali metal hydroxide solutions. Such very good solubility can be seen, e. g., in a temperature range of from zero ° C. to 40° C., in particular at room temperature and/or at zero and/or +10° C.

Another aspect of the present invention is therefore an aqueous solution of an inventive mixture, containing in the range of from 43 to 70% by weight of said inventive mixture, preferably 45 to 65% by weight, even more preferably 48 to 60% by weight. Such aqueous solutions are hereinafter also being referred to as inventive solutions or solutions according to the present invention. Inventive solutions do not show amounts of precipitation or crystallization on addition of seed crystals or mechanical stress at ambient temperature. Inventive solutions do not exhibit any visible turbidity.

In a preferred embodiment of the present invention, solutions according to the present invention are free from surfactants. Free from surfactants shall mean, in the context of the present invention, that the total contents of surfactants is 0.1% by weight or less, referring to the amount of inventive mixture. In a preferred embodiment, the term “free from surfactants” shall encompass a concentration in the range of from 50 ppm to 0.05%, both ppm and % referring to ppm by weight or % by weight, respectively, and referring to the total respective inventive solution.

In a preferred embodiment of the present invention, solutions according to the present invention are free from organic polymers. Free from organic polymers shall mean, in the context of the present invention, that the total contents of organic polymers is 0.1% by weight or less, referring to the amount of inventive mixture. In a preferred embodiment, the term “free from organic polymers” shall encompass a concentration in the range of from 50 ppm to 0.05%, both ppm and % referring to ppm by weight or % by weight, respectively, and referring to the total respective inventive solution. Organic polymers shall also include organic copolymers and shall include polyacrylates, polyethylene imines, and polyvinylpyrrolidone. Organic (co)polymers in the context of the present invention shall have a molecular weight (M_(w)) of 1,000 g or more.

In a preferred embodiment of the present invention, inventive solutions do not contain major amounts of alkali metal salts of mono- and dicarboxylic acids such as acetic acid, propionic acid, maleic acid, acrylic acid, adipic acid, succinic acid, and the like. Major amounts in this context refer to amounts over 0.8% by weight.

In one embodiment of the present invention, inventive solutions have a pH value in the range of from 8 to 14, preferably 10.0 to 13.5.

In one embodiment of the present invention, inventive solutions additionally contain at least one inorganic basic salt selected from alkali metal hydroxides and alkali metal carbonates. Preferred examples are sodium carbonate, potassium carbonate, potassium hydroxide and in particular sodium hydroxide, for example 0.1 to 1.5% by weight. Potassium hydroxide or sodium hydroxide, respectively, may result from the manufacture of the respective inventive solution.

Furthermore, inventive mixtures as well as inventive solutions may contain one or more inorganic non-basic salts such as—but not limited to—alkali metal halide or preferably alkali metal sulphate, especially potassium sulphate or even more preferably sodium sulphate. The content of inorganic non-basic salt may be in the range of from 0.10 to 1.5% by weight, referring to the respective inventive mixture or the solids content of the respective inventive solution. Even more preferably, inventive mixtures as well as inventive solutions do not contain significant amounts of inorganic non-basic salt, for example in the range of from 50 ppm to 0.05% by weight, referring to the respective inventive mixture or the solids content of the respective inventive solution. Even more preferably, inventive mixtures contain 1 to 50 ppm by weight of sum of chloride and sulphate, referring to the respective inventive mixture. The contents of sulphate may be determined, for example, by gravimetric analysis or by ion chromatography.

Furthermore, inventive mixtures as well as inventive solutions exhibit advantageous olfactory behaviour as well as a very low tendency to colorize such as yellowing upon storage.

Inventive mixtures may be prepared by mixing the respective quantities MGDA or its respective salt(s) with component (B). However, the separate manufacture of components (A) and (B) is tedious, and other processes of making inventive mixtures have been found in the context of the present invention.

A further aspect of the present invention is a process for making inventive mixtures, hereinafter also being referred to as inventive process. The inventive process comprises the steps of

-   -   (a) dissolving a mixture of alanine and aspartate in water or an         aqueous solution of an alkali metal hydroxide,     -   (b) converting the respective dissolved amino acids and their         respective alkali metal salts with formaldehyde and hydrocyanic         acid or alkali metal cyanide to the respective dinitriles,     -   (c) saponification of the dinitriles resulting from step (b),         employing stoichiometric amounts of hydroxide or an excess of         1.01 to 1.5 moles of hydroxide per molar sum of COOH groups and         nitrile groups of dinitrile from step (b).

The inventive process will be described in more detail below.

Aspartic acid may be used as racemic mixture or as enantiomerically enriched mixture or as enantiomerically pure L-amino acid.

In step (a) of the inventive process, a mixture of alanine and aspartic acid is being dissolved in water or an aqueous solution of an alkali metal hydroxide, in the form of the pure acids or as partially neutralized acids. L-alanine in the context of the present invention refers to any mixture of enantiomers of alanine, for example to racemic alanine or to either pure L-alanine with non-detectable amounts of D-alanine, or to mixtures of enantiomers of L-alanine and D-alanine, the enantiomeric excess being at least 96%, preferably at least 98%. Preferred is racemic alanine, hereinafter also D,L-alanine.

In one embodiment of the present invention, mixtures from alanine and aspartic acid may be prepared by mixing such amino acids in the desired quantities, in the absence or presence of water.

In an alternative embodiment of the present invention, mixtures from L-alanine and aspartic may be obtained by synthesizing alanine in the presence of at least one or more enzyme that decarboxylates aspartic acid followed by subsequent removal or destroying of said enzyme and incomplete purification of the alanine so obtained.

Of the alkali metal hydroxide, potassium hydroxide is preferred and sodium hydroxide is even more preferred. Mixtures from two or more different alkali metal hydroxides are feasible as well, for example mixtures from sodium hydroxide and potassium hydroxide.

There are various ways to perform step (a) of the inventive process. It is possible to prepare a solid mixture of alanine and the alkali metal salt of alanine and to then dissolve the mixture so obtained in water, followed by addition of aspartate. It is preferred, though, to slurry L-alanine in water and to then add the required amount of alkali metal hydroxide, as solid or as aqueous solution.

In one embodiment of the present invention, step (a) of the inventive process is being carried out at a temperature in the range of from 5 to 70° C., preferably in the range of from 15 to 60° C. During the performance of step (a), in many instances a raise of temperature can be observed, especially when the embodiment of slurrying alanine and aspartate in water and to then add the required amount of alkali metal hydroxide, as solid or as aqueous solution, has been chosen.

An aqueous solution of a mixture of alanine and aspartate and the corresponding alkali metal salts will be obtained from step (a).

In one embodiment of step (a), an aqueous solution of a mixture of the range of from 10 to 50 mole-% of alanine (free acid) and of 50 to 90 mole-% of alanine (alkali metal salt) and a respective ratio of aspartic acid and aspartate is being obtained. Particularly preferred are mixtures of 23 to 27 mole-% of D,L-alanine (free acid) and 63 to 67 mole-% of the alkali metal salt of D,L-alanine and aspartic acid/aspartate. The solution obtained in accordance with step (a) is hereinafter also being referred to as “the amino acids solution”.

Preferably, the amino acids solution may have a total solids content in the range of from 10 to 35%. Preferably, such aqueous solution of a mixture of L-alanine and aspartate and their corresponding alkali metal salts may have a pH value in the range of from 6 to 12.

Preferably, the amino acids solution contains less than 0.5% by weight impurities, the percentage being based on the total solids content of the aqueous solution. Such potential impurities may be one or more of magnesium or calcium salts of inorganic acids. Trace amounts of impurities stemming from the L-alanine or the water used shall be neglected in the further context with the present invention.

In step (b) of the inventive process, a double Strecker synthesis is carried out by treating the amino acids solution with formaldehyde and hydrocyanic acid or alkali metal cyanide. The double Strecker synthesis may be carried out by adding alkali metal cyanide or a mixture from hydrocyanic acid and alkali metal cyanide or preferably hydrocyanic acid and formaldehyde to the amino acids solution. Said addition of formaldehyde and alkali metal cyanide or preferably hydrocyanic acid can be performed in one or more portions. Formaldehyde can be added as gas or as formalin solution or as paraformaldehyde. Preferred is the addition of formaldehyde as 30 to 35% by weight aqueous solution.

In a particular embodiment of the present invention, step (b) of the inventive process is carried out at a temperature in the range of from 20 to 80° C., preferably from 35 to 65° C.

In one embodiment of the present invention, step (b) of the inventive process is carried out at a constant temperature in the above range. In another embodiment, step (b) of the inventive process is carried out using a temperature profile, for example by starting the reaction at 40° C. and allowing then stirring the reaction mixture at 50° C.

In one embodiment of the present invention, step (b) of the inventive process is being carried out at elevated pressure, for example 1.01 to 6 bar. In another embodiment, step (b) of the inventive process is being carried at normal pressure (1 bar).

In one embodiment of the present invention, step (b) of the inventive process is being carried out at a constant pH value, and a base or an acid is being added in order to keep the pH value constant. Preferably, however, the pH value during step (b) is decreasing, and neither base nor acid other than, optionally, HCN is being added. In such embodiments, at the end of step (b), the pH value may have dropped to 2 to 4.

Step (b) can be performed in any type of reaction vessel that allows the handling of hydrocyanic acid. Useful are, for example, flasks, stirred tank reactors and cascades of two or more stirred tank reactors.

From step (b), an aqueous solution of a mixture of the L-enantiomers, dinitriles of the below formulae

and their corresponding alkali metal salts will be obtained, briefly also referred to as “the dinitriles” or “the alkali metal salts of the dinitriles”, respectively.

In step (c), the dinitriles are saponified, employing stoichiometric amounts of hydroxide or an excess of 1.01 to 1.5 moles of hydroxide per molar sum of COOH groups and nitrile groups of the dinitriles, preferably 1.01 to 1.2 moles. Said saponification may be carried out in one or more steps, for example in two steps. In embodiments wherein the saponification is carried out in one step, the temperature is in the range of from 75 to 200° C., preferably 95 to 125° C.

In other embodiments, the saponification is carried out in at least two different steps, (c1) and (c2) and, for example, optionally a step (c3), said different steps being carried out at different temperatures.

Different temperature means in the context of step (c) that the average temperature of step (c1) is different from the average temperature of step (c2). Preferably, step (c1) is being performed at a temperature lower than step (c2). Even more preferably, step (c2) is being performed at an average temperature that is at least 20° C. higher than the average temperature of step (c1). In some embodiments, step (c2) is performed at an average temperature that is at least 100° C. higher than the average temperature of step (c1). Hydroxide in the context of step (c) refers to alkali metal hydroxide, preferably potassium hydroxide or mixtures from potassium hydroxide and sodium hydroxide and even more preferably to sodium hydroxide.

Step (c1) can be started by adding the solution of the nitriles (b) to an aqueous solution of alkali metal hydroxide or adding an aqueous solution of alkali metal hydroxide to a solution of the nitriles (b). In another embodiment, the solution resulting from step (b) and an aqueous solution of alkali metal hydroxide are being added simultaneously to a vessel.

When calculating the stoichiometric amounts of hydroxide to be added in step (c1), the sum of COOH groups and nitrile groups from the total theoretical amount of dinitriles is multiplied by 3 and the amounts of alkali already present from step (a) and, optionally, step (b), is subtracted.

Step (c1) may be performed at a temperature in the range of from 20 to 80° C., preferable 40 to 70° C. In the context of step (c1) “temperature” refers to the average temperature.

As a result of step (c1), an aqueous solution of the respective diamides and their respective alkali metals salt can be obtained, M being alkali metal. Said solution may also contain L-MGDA and the corresponding monoamide and/or its mono- or dialkali metal salt.

Step (c2) may be performed at a temperature in the range of from 80 to 200° C., preferably 175 to 195° C. In the context of step (c2) “temperature” refers to the average temperature.

In one embodiment of the present invention, step (c2) has an average residence time in the range of from 5 to 180 minutes.

In preferred embodiments the higher range of the temperature interval of step (c2) such as 190 to 200° C. is combined with a short residence time such as 15 to 25 minutes, or a middle range of the temperature interval of step (c2) such as 175° C. to 180° C. is combined with a longer residence time such as 25 to 60 minutes, or a specific temperature such as 185° C. is combined with a middle residence time such as 20 to 45 minutes, or a temperature in the range of from 80 to 110° C. with a residence time in the range of from 4 to 10 hours.

In one embodiment of the present invention, step (c1) is carried out at a temperature in the range of from 20 to 80° C. and step (c2) is carried out at a temperature in the range of from 80 to 200° C., the temperature in step (c2) being higher than in step (c1). It is thus possible to perform step (c1) at a temperature in the range of from 20 to 60° C. and step (c2) at a temperature in the range of from 80 to 200° C., preferable 85 to 120° C. It is also possible to perform step (c1) at a temperature in the range of from 60 to 80° C. and step (c2) at a temperature in the range of from 110° C. up to 200° C., preferably up to 190° C.

Step (c2) can be performed in the same reactor as step (c1), or—in the case of a continuous process—in a different reactor.

In one embodiment of the present invention step (c2) is carried out with an excess of base of 1.01 to 1.2 moles of hydroxide per mole of nitrile group.

Depending on the type of reactor in which step (c2) is being performed, such as an ideal plug flow reactor, the average residence time can be replaced by the residence time.

In one embodiment of the present invention, step (c1) is being carried out in a continuous stirred tank reactor and step (c2) is being carried out in a second continuous stirred tank reactor. In a preferred embodiment, step (c1) is being carried out in a continuous stirred tank reactor and step (c2) is being carried out in a plug flow reactor, such as a tubular reactor.

In one embodiment of the present invention, step (c1) of the inventive process is being carried out at elevated pressure, for example at 1.05 to 6 bar. In another embodiment, step (c1) of the inventive process is being carried at normal pressure.

Especially in embodiments wherein step (c2) is being carried out in a plug flow reactor, step (c2) may be carried out at elevated pressure such as 1.5 to 40 bar, preferably at least 20 bar. The elevated pressure may be accomplished with the help of a pump or by autogenic pressure elevation.

Preferably, the pressure conditions of steps (c1) and (c2) are combined in the way that step (c2) is carried out at a higher pressure than step (c1).

Depending on the reaction temperature and the starting material, a partial racemization may take place during step (c2). Without wishing to be bound by any theory, it is likely that any racemization to occur is taking place on the stage of an L-diamide or of L-MGDA, and on the stage of the diamide of or of the resulting diacetic acid derivative of aspartate.

In one embodiment of the present invention, the inventive process may comprise additional steps other than steps (a), (b) and (c) disclosed above. Such additional steps may be, for example, one or more decolourization steps, for example with activated carbon or with peroxide such as H₂O₂.

A further step other than step (a), (b) or (c) that is preferably carried out after step (c2) is stripping with nitrogen or steam in order to remove ammonia. Said stripping can be carried out at temperatures in the range of from 90 to 110° C. By nitrogen or air stripping, water can be removed from the solution so obtained. Stripping is preferably carried out at a pressure below normal pressure, such as 650 to 950 mbar.

In embodiments wherein an inventive solution is desired, the solution obtained from step (c2) is just cooled down and, optionally, concentrated by partially removing the water. If dry samples of inventive mixtures are required, the water can be removed by spray drying or spray granulation.

The inventive process may be carried out as a batch process, or as a semi-continuous or continuous process.

A further aspect of the present invention is the use of an inventive mixture or an inventive solution for the manufacture of laundry detergent compositions and of detergent compositions for cleaners. A further aspect is a process for manufacture of laundry detergents and of detergent compositions cleaners by using an inventive mixture or an inventive solution. Depending on whether a mixing in aqueous formulation or in dry matter is desired, and depending on whether a liquid or solid detergent composition is desired, an inventive aqueous solution or an inventive mixture of isomers can be used. Mixing can be performed by formulation steps known per se.

In particular when mixing is being carried out with an inventive solution for the production of a solid laundry detergent compositions or a solid detergent composition for cleaners, such use is advantageous because it allows to add only reduced amounts of water to be removed later, and it allows for great flexibility because no additional ingredients such as polymer, surfactants or salts are present that otherwise reduce flexibility of the detergent manufacturer.

In one embodiment of the present invention, inventive aqueous solutions may be used as such for the manufacture of laundry detergent compositions or for detergent compositions for cleaners.

In other embodiments, inventive aqueous solutions may be used in fully or preferably partially neutralized form for the manufacture of laundry detergent compositions or for detergent compositions for cleaners. In one embodiment, inventive aqueous solutions may be used in fully or preferably partially neutralized form for the manufacture of laundry detergent compositions or of detergent compositions for cleaners, said neutralization being performed with an inorganic acid (mineral acid). Preferred inorganic acids are selected from H₂SO₄, HCl, and H₃PO₄. In other embodiments, inventive aqueous solutions may be used in fully or preferably partially neutralized form for the manufacture of laundry detergent compositions or of detergent compositions for cleaners, said neutralization being performed with an organic acid. Preferred organic acids are selected from CH₃SO₃H, acetic acid, propionic acid, and citric acid.

In the context of the present invention, the term “detergent composition for cleaners” includes cleaners for home care and for industrial or institutional applications. The term “detergent composition for cleaners” includes compositions for dishwashing, especially hand dishwash and automatic dishwashing and ware-washing, and compositions for hard surface cleaning such as, but not limited to compositions for bathroom cleaning, kitchen cleaning, floor cleaning, descaling of pipes, window cleaning, car cleaning including truck cleaning, furthermore, open plant cleaning, cleaning-in-place, metal cleaning, disinfectant cleaning, farm cleaning, high pressure cleaning, but not laundry detergent compositions.

In the context of the present invention and unless expressly stated otherwise, percentages in the context of ingredients of laundry detergent compositions are percentages by weight and refer to the total solids content of the respective laundry detergent composition. In the context of the present invention and unless expressly stated otherwise, percentages in the context of ingredients of detergent composition for cleaners are percentages by weight and refer to the total solids content of the detergent composition for cleaner.

In one embodiment of the present invention, laundry detergent compositions according to the present invention may contain in the range of from 1 to 30% by weight of inventive mixture. Percentages refer to the total solids content of the respective laundry detergent composition.

In one embodiment of the present invention, detergent compositions for cleaners according to the present invention may contain in the range of from 1 to 50% by weight of inventive mixture, preferably 5 to 40% by weight and even more preferably 10 to 25% by weight. Percentages refer to the total solids content of the respective detergent composition for home care.

Particularly advantageous laundry detergent compositions and of detergent compositions for cleaners, especially for home care may contain one or more complexing agent other than MGDA. Advantageous detergent compositions for cleaners and advantageous laundry detergent compositions may contain one or more complexing agent (in the context of the present invention also referred to as sequestrant) other than a mixture according to the present invention. Examples for sequestrants other than a mixture according to the present invention are GLDA, IDS (iminodisuccinate), IDA (iminodiacetate), citrate, phosphonic acid derivatives, for example the disodium salt of hydroxyethane-1,1-diphosphonic acid (“HEDP”), and polymers with complexing groups like, for example, polyethyleneimine in which 20 to 90 mole-% of the N-atoms bear at least one CH₂COO— group, and their respective alkali metal salts, especially their sodium salts, for example GLDA-Na₄, IDS-NA₄, and trisodium citrate, and phosphates such as STPP (sodium tripolyphosphate). Due to the fact that phosphates raise environmental concerns, it is preferred that advantageous detergent compositions for cleaners and advantageous laundry detergent compositions are free from phosphate. “Free from phosphate” should be understood in the context of the present invention, as meaning that the content of phosphate and polyphosphate is in sum in the range from 10 ppm to 0.2% by weight, determined by gravimetric analysis.

Advantageous detergent compositions for cleaners and advantageous laundry detergent compositions may contain one or more surfactant, preferably one or more non-ionic surfactant.

Preferred non-ionic surfactants are alkoxylated alcohols, di- and multiblock copolymers of ethylene oxide and propylene oxide and reaction products of sorbitan with ethylene oxide or propylene oxide, alkyl polyglycosides (APG), hydroxyalkyl mixed ethers and amine oxides.

Preferred examples of alkoxylated alcohols and alkoxylated fatty alcohols are, for example, compounds of the general formula (III)

in which the variables are defined as follows:

-   -   R¹ is identical or different and selected from hydrogen and         linear C₁-C₁₀-alkyl, preferably in each case identical and ethyl         and particularly preferably hydrogen or methyl,     -   R² is selected from C₈-C₂₂-alkyl, branched or linear, for         example n-C₈H₁₇, n-C₁₀H₂₁, n-C₁₂H₂₅, n-C₁₄H₂₉, n-C₁₆H₃₃ or         n-C₁₈H₃₇,     -   R³ is selected from C₁-C₁₀-alkyl, methyl, ethyl, n-propyl,         isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl,         isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl,         n-hexyl, isohexyl, sec-hexyl, n-heptyl, n-octyl, 2-ethylhexyl,         n-nonyl, n-decyl or isodecyl,

m and n are in the range from zero to 300, where the sum of n and m is at least one, preferably in the range of from 3 to 50. Preferably, m is in the range from 1 to 100 and n is in the range from 0 to 30.

In one embodiment, compounds of the general formula (III) may be block copolymers or random copolymers, preference being given to block copolymers.

Other preferred examples of alkoxylated alcohols are, for example, compounds of the general formula (IV)

in which the variables are defined as follows:

-   -   R¹ is identical or different and selected from hydrogen and         linear C₁-C₁₀-alkyl, preferably identical in each case and ethyl         and particularly preferably hydrogen or methyl,     -   R⁴ is selected from C₆-C₂₀-alkyl, branched or linear, in         particular n-C₈H₁₇, n-C₁₀H₂₁, n-C₁₂H₂₅, n-C₁₃H₂₇, n-C₁₅H₃₁,         n-C₁₄H₂₉, n-C₁₆H₃₃, n-C₁₈H₃₇,     -   a is a number in the range from zero to 10, preferably from 1 to         6,     -   b is a number in the range from 1 to 80, preferably from 4 to         20,     -   d is a number in the range from zero to 50, preferably 4 to 25.

The sum a+b+d is preferably in the range of from 5 to 100, even more preferably in the range of from 9 to 50.

Preferred examples for hydroxyalkyl mixed ethers are compounds of the general formula (V)

in which the variables are defined as follows:

-   -   R¹ is identical or different and selected from hydrogen and         linear C₁-C₁₀-alkyl, preferably in each case identical and ethyl         and particularly preferably hydrogen or methyl,     -   R² is selected from C₈-C₂₂-alkyl, branched or linear, for         example iso-C₁₁H₂₃, iso-C₁₃H₂₇, n-C₈H₁₇, n-C₁₀H₂₁, n-C₁₂H₂₅,         n-C₁₄H₂₉, n-C₁₆H₃₃ or n-C₁₈H₃₇,     -   R³ is selected from C₁-C₁₈-alkyl, methyl, ethyl, n-propyl,         isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl,         isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl,         n-hexyl, isohexyl, sec-hexyl, n-heptyl, n-octyl, 2-ethylhexyl,         n-nonyl, n-decyl, isodecyl, n-dodecyl, n-tetradecyl,         n-hexadecyl, and n-octadecyl.

The integers m and n are in the range from zero to 300, where the sum of n and m is at least one, preferably in the range of from 5 to 50. Preferably, m is in the range from 1 to 100 and n is in the range from 0 to 30.

Compounds of the general formula (IV) and (V) may be block copolymers or random copolymers, preference being given to block copolymers.

Further suitable nonionic surfactants are selected from di- and multiblock copolymers, composed of ethylene oxide and propylene oxide. Further suitable nonionic surfactants are selected from ethoxylated or propoxylated sorbitan esters. Amine oxides or alkyl polyglycosides, especially linear C₄-C₁₆-alkyl polyglucosides and branched C₈-C₁₄-alkyl polyglycosides such as compounds of general average formula (VI) are likewise suitable.

wherein:

-   -   R⁵ is C₁-C₄-alkyl, in particular ethyl, n-propyl or isopropyl,     -   R⁶ is —(CH₂)₂—R⁵,     -   G¹ is selected from monosaccharides with 4 to 6 carbon atoms,         especially from glucose and xylose,     -   y in the range of from 1.1 to 4, y being an average number.

Further examples of non-ionic surfactants are compounds of general formula (VII) and (VIII)

AO is selected from ethylene oxide, propylene oxide and butylene oxide,

EO is ethylene oxide, CH₂CH₂—O,

R⁷ selected from C₈-C₁₈-alkylbranched or linear

A³O is selected from propylene oxide and butylene oxide,

w is a number in the range of from 15 to 70, preferably 30 to 50,

w1 and w3 are numbers in the range of from 1 to 5, and

w2 is a number in the range of from 13 to 35.

An overview of suitable further nonionic surfactants can be found in EP-A 0 851 023 and in DEA 198 19 187.

Mixtures of two or more different nonionic surfactants may also be present.

Other surfactants that may be present are selected from amphoteric (zwitterionic) surfactants and anionic surfactants and mixtures thereof.

Examples of amphoteric surfactants are those that bear a positive and a negative charge in the same molecule under use conditions. Preferred examples of amphoteric surfactants are so-called betaine-surfactants. Many examples of betaine-surfactants bear one quaternized nitrogen atom and one carboxylic acid group per molecule. A particularly preferred example of amphoteris surfactants is cocamidopropyl betaine (lauramidopropyl betaine).

Examples of amine oxide surfactants are compounds of the general formula (IX) R⁸R⁹R¹⁰N→O  (IX)

wherein R¹⁰, R⁸ and R⁹ are selected independently from each other from aliphatic, cycloaliphatic or C₂-C₄-alkylene C₁₀-C₂₀-alkylamido moieties. Preferably, R¹⁰ is selected from C₈-C₂₀-alkyl or C₂-C₄-alkylene C₁₀-C₂₀-alkylamido and R⁸ and R⁹ are both methyl.

A particularly preferred example is lauryl dimethyl aminoxide, sometimes also called lauramine oxide. A further particularly preferred example is cocamidylpropyl dimethylaminoxide, sometimes also called cocamidopropylamine oxide.

Examples of suitable anionic surfactants are alkali metal and ammonium salts of C₈-C₁₈-alkyl sulfates, of C₈-C₁₈-fatty alcohol polyether sulfates, of sulfuric acid half-esters of ethoxylated C₄-C₁₂-alkylphenols (ethoxylation: 1 to 50 mol of ethylene oxide/mol), C₁₂-C₁₈ sulfo fatty acid alkyl esters, for example of C₁₂-C₁₈ sulfo fatty acid methyl esters, furthermore of C₁₂-C₁₈-alkylsulfonic acids and of C₁₀-C₁₈-alkylarylsulfonic acids. Preference is given to the alkali metal salts of the aforementioned compounds, particularly preferably the sodium salts.

Further examples for suitable anionic surfactants are soaps, for example the sodium or potassium salts of stearic acid, oleic acid, palmitic acid, ether carboxylates, and alkylether phosphates.

Preferably, laundry detergent compositions contain at least one anionic surfactant.

In one embodiment of the present invention, laundry detergent compositions may contain 0.1 to 60% by weight of at least one surfactant, selected from anionic surfactants, amphoteric surfactants and amine oxide surfactants.

In one embodiment of the present invention, detergent compositions for cleaners may contain 0.1 to 60% by weight of at least one surfactant, selected from anionic surfactants, amphoteric surfactants and amine oxide surfactants.

In a preferred embodiment, detergent compositions for cleaners and especially those for automatic dishwashing do not contain any anionic surfactant.

Detergent compositions for cleaners and laundry detergent compositions may contain at least one bleaching agent, also referred to as bleach. Bleaching agents may be selected from chlorine bleach and peroxide bleach, and peroxide bleach may be selected from inorganic peroxide bleach and organic peroxide bleach. Preferred are inorganic peroxide bleaches, selected from alkali metal percarbonate, alkali metal perborate and alkali metal persulfate.

In solid detergent compositions for hard surface cleaning and in inventive solid laundry detergent compositions, alkali metal percarbonates, especially sodium percarbonates, are preferably used in coated form. Such coatings may be of organic or inorganic nature. Examples are glycerol, sodium sulfate, silicate, sodium carbonate, and combinations of at least two of the foregoing, for example combinations of sodium carbonate and sodium sulfate.

Examples of organic bleaching agents are percarboxylic acids.

Suitable chlorine-containing bleaches are, for example, 1,3-dichloro-5,5-dimethylhydantoin, N-chlorosulfamide, chloramine T, chloramine B, sodium hypochlorite, calcium hypochlorite, magnesium hypochlorite, potassium hypochlorite, potassium dichloroisocyanurate and sodium dichloroisocyanurate.

Detergent compositions for cleaners and laundry detergent compositions may comprise, for example, in the range from 3 to 10% by weight of chlorine-containing bleach.

Detergent compositions for cleaners and laundry detergent compositions may comprise one or more bleach catalysts. Bleach catalysts can be selected from bleach-boosting transition metal salts or transition metal complexes such as, for example, manganese-, iron-, cobalt-, ruthenium- or molybdenum-salen complexes or carbonyl complexes. Manganese, iron, cobalt, ruthenium, molybdenum, titanium, vanadium and copper complexes with nitrogen-containing tripod ligands and also cobalt-, iron-, copper- and ruthenium-amine complexes can also be used as bleach catalysts.

Detergent compositions for cleaners and laundry detergent compositions may comprise one or more bleach activators, for example N-methylmorpholinium-acetonitrile salts (“MMA salts”), trimethylammonium acetonitrile salts, N-acylimides such as, for example, N-nonanoylsuccinimide, 1,5-diacetyl-2,2-dioxohexahydro-1,3,5-triazine (“DADHT”) or nitrile quats (trimethylammonium acetonitrile salts).

Further examples of suitable bleach activators are tetraacetylethylenediamine (TAED) and tetraacetylhexylenediamine.

Detergent compositions for cleaners and laundry detergent compositions may comprise one or more corrosion inhibitors. In the present case, this is to be understood as including those compounds which inhibit the corrosion of metal. Examples of suitable corrosion inhibitors are triazoles, in particular benzotriazoles, bisbenzotriazoles, aminotriazoles, alkylaminotriazoles, also phenol derivatives such as, for example, hydroquinone, pyrocatechol, hydroxyhydroquinone, gallic acid, phloroglucinol or pyrogallol.

In one embodiment of the present invention, detergent compositions for cleaners and laundry detergent compositions comprise in total in the range from 0.1 to 1.5% by weight of corrosion inhibitor.

Detergent compositions for cleaners and laundry detergent compositions may comprise one or more builders, selected from organic and inorganic builders. Examples of suitable inorganic builders are sodium sulfate or sodium carbonate or silicates, in particular sodium disilicate and sodium metasilicate, zeolites, sheet silicates, in particular those of the formula α-Na₂Si₂O₅, β-Na₂Si₂O₅, and δ-NA₂Si₂O₅, also fatty acid sulfonates, α-hydroxypropionic acid, alkali metal malonates, fatty acid sulfonates, alkyl and alkenyl disuccinates, tartaric acid diacetate, tartaric acid monoacetate, oxidized starch, and polymeric builders, for example polycarboxylates and polyaspartic acid.

Examples of organic builders are especially polymers and copolymers. In one embodiment of the present invention, organic builders are selected from polycarboxylates, for example alkali metal salts of (meth)acrylic acid homopolymers or (meth)acrylic acid copolymers.

Suitable comonomers are monoethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, maleic anhydride, itaconic acid and citraconic acid. A suitable polymer is in particular polyacrylic acid, which preferably has an average molecular weight M_(w) in the range from 2000 to 40 000 g/mol, preferably 2000 to 10 000 g/mol, in particular 3000 to 8000 g/mol. Also of suitability are copolymeric polycarboxylates, in particular those of acrylic acid with methacrylic acid and of acrylic acid or methacrylic acid with maleic acid and/or fumaric acid, and in the same range of molecular weight.

It is also possible to use copolymers of at least one monomer from the group consisting of monoethylenically unsaturated C₃-C₁₀-mono- or C₄-C₁₀-dicarboxylic acids or anhydrides thereof, such as maleic acid, maleic anhydride, acrylic acid, methacrylic acid, fumaric acid, itaconic acid and citraconic acid, with at least one hydrophilic or hydrophobic monomer as listed below.

Suitable hydrophobic monomers are, for example, isobutene, diisobutene, butene, pentene, hexene and styrene, olefins with 10 or more carbon atoms or mixtures thereof, such as, for example, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-docosene, 1-tetracosene and 1-hexacosene, C₂₂-α-olefin, a mixture of C₂₀-C₂₄-α-olefins and polyisobutene having on average 12 to 100 carbon atoms per molecule.

Suitable hydrophilic monomers are monomers with sulfonate or phosphonate groups, and also nonionic monomers with hydroxyl function or alkylene oxide groups. By way of example, mention may be made of: allyl alcohol, isoprenol, methoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, methoxypolybutylene glycol (meth)acrylate, methoxypoly(propylene oxide-co-ethylene oxide) (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, ethoxypolypropylene glycol (meth)acrylate, ethoxypolybutylene glycol (meth)acrylate and ethoxypoly(propylene oxide-co-ethylene oxide) (meth)acrylate. Polyalkylene glycols here may comprise 3 to 50, in particular 5 to 40 and especially 10 to 30 alkylene oxide units per molecule.

Particularly preferred sulfonic-acid-group-containing monomers here are 1-acrylamido-1-propanesulfonic acid, 2-acrylamido-2-propanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 3-methacrylamido-2-hydroxypropanesulfonic acid, allylsulfonic acid, methallylsulfonic acid, allyloxybenzenesulfonic acid, methallyloxybenzenesulfonic acid, 2-hydroxy-3-(2-propenyloxy) propanesulfonic acid, 2-methyl-2-propene-1-sulfonic acid, styrenesulfonic acid, vinylsulfonic acid, 3-sulfopropyl acrylate, 2-sulfoethyl methacrylate, 3-sulfopropyl methacrylate, sulfomethacrylamide, sulfomethylmethacrylamide, and salts of said acids, such as sodium, potassium or ammonium salts thereof.

Particularly preferred phosphonate-group-containing monomers are vinylphosphonic acid and its salts.

Moreover, amphoteric polymers can also be used as builders.

Detergent compositions for cleaners and laundry detergent compositions according to the invention may comprise, for example, in the range from in total 10 to 70% by weight, preferably up to 50% by weight, of builder. In the context of the present invention, MGDA is not counted as builder.

In one embodiment of the present invention, detergent compositions for cleaners and laundry detergent compositions according to the invention may comprise one or more cobuilders.

Detergent compositions for cleaners and laundry detergent compositions may comprise one or more antifoams, selected for example from silicone oils and paraffin oils.

In one embodiment of the present invention, detergent compositions for cleaners and laundry detergent compositions comprise in total in the range from 0.05 to 0.5% by weight of antifoam.

Detergent compositions for cleaners and laundry detergent according to the invention may comprise one or more enzymes. Examples of enzymes are lipases, hydrolases, amylases, proteases, cellulases, esterases, pectinases, lactases and peroxidases.

In one embodiment of the present invention, detergent compositions for cleaners and laundry detergent compositions according to the present invention may comprise, for example, up to 5% by weight of enzyme, preference being given to 0.1 to 3% by weight. Said enzyme may be stabilized, for example with the sodium salt of at least one C₁-C₃-carboxylic acid or C₄-C₁₀-dicarboxylic acid. Preferred are formates, acetates, adipates, and succinates.

In one embodiment of the present invention, detergent compositions for cleaners and laundry detergent compositions according to the invention comprise at least one zinc salt. Zinc salts can be selected from water-soluble and water-insoluble zinc salts. In this connection, within the context of the present invention, water-insoluble is used to refer to those zinc salts which, in distilled water at 25° C., have a solubility of 0.1 g/l or less. Zinc salts which have a higher solubility in water are accordingly referred to within the context of the present invention as water-soluble zinc salts.

In one embodiment of the present invention, zinc salt is selected from zinc benzoate, zinc gluconate, zinc lactate, zinc formate, ZnCl₂, ZnSO₄, zinc acetate, zinc citrate, Zn(NO₃)₂, Zn(CH₃SO₃)₂ and zinc gallate, preferably ZnCl₂, ZnSO₄, zinc acetate, zinc citrate, Zn(NO₃)₂, Zn(CH₃SO₃)₂ and zinc gallate.

In another embodiment of the present invention, zinc salt is selected from ZnO, ZnO·aq, Zn(OH)₂ and ZnCO₃. Preference is given to ZnO·aq.

In one embodiment of the present invention, zinc salt is selected from zinc oxides with an average particle diameter (weight-average) in the range from 10 nm to 100 μm.

The cation in zinc salt can be present in complexed form, for example complexed with ammonia ligands or water ligands, and in particular be present in hydrated form. To simplify the notation, within the context of the present invention, ligands are generally omitted if they are water ligands.

Depending on how the pH of mixture according to the invention is adjusted, zinc salt can change. Thus, it is for example possible to use zinc acetate or ZnCl2 for preparing formulation according to the invention, but this converts at a pH of 8 or 9 in an aqueous environment to ZnO, Zn(OH)₂ or ZnO·aq, which can be present in non-complexed or in complexed form.

Zinc salt is preferably present in the form of particles in those detergent compositions for cleaners according to the invention which are solid at room temperature. Such particles may have an average diameter (number-average) in the range from 10 nm to 100 μm, preferably 100 nm to 5 μm, determined for example by X-ray scattering.

Zinc salt may be present in those detergent compositions for home which are liquid at room temperature in dissolved or in solid or in colloidal form.

In one embodiment of the present invention, detergent compositions for cleaners and laundry detergent compositions comprise in total in the range from 0.05 to 0.4% by weight of zinc salt, based in each case on the solids content of the composition in question.

Here, the fraction of zinc salt is given as zinc or zinc ions. From this, it is possible to calculate the counterion fraction.

In one embodiment of the present invention, detergent compositions for cleaners and laundry detergent compositions according to the invention are free from heavy metals apart from zinc compounds. Within the context of the present, this may be understood as meaning that detergent compositions for cleaners and laundry detergent compositions according to the invention are free from those heavy metal compounds which do not act as bleach catalysts, in particular of compounds of iron and of bismuth. Within the context of the present invention, “free from” in connection with heavy metal compounds is to be understood as meaning that the content of heavy metal compounds which do not act as bleach catalysts is in sum in the range from 0 to 100 ppm, determined by the leach method and based on the solids content. Preferably, formulation according to the invention has, apart from zinc, a heavy metal content below 0.05 ppm, based on the solids content of the formulation in question. The fraction of zinc is thus not included.

Within the context of the present invention, “heavy metals” are deemed to be all metals with a specific density of at least 6 g/cm³ with the exception of zinc. In particular, the heavy metals are metals such as bismuth, iron, copper, lead, tin, nickel, cadmium and chromium.

Preferably, detergent compositions for cleaners and laundry detergent compositions according to the invention comprise no measurable fractions of bismuth compounds, i.e. for example less than 1 ppm.

In one embodiment of the present invention, detergent compositions according to the present invention comprise one or more further ingredient such as fragrances, dyestuffs, organic solvents, buffers, disintegrants for tabs, and/or acids such as methylsulfonic acid.

Preferred example detergent compositions for automatic dishwashing may be selected according to table 1.

TABLE 1 Example detergent compositions for automatic dishwashing All amounts in g/sample ADW.1 ADW.2 ADW.3 inventive mixture, 99.75 wt % 30 22.5 15 racemic MGDA-Na₃ + 0.25 wt % of aspa-DA-Na₄ protease 2.5 2.5 2.5 amylase 1 1 1 n-C₁₈H₃₇—O(CH₂CH₂O)₉H 5 5 5 Polyacrylic acid M_(w) 4000 g/mol as 10 10 10 sodium salt, completely neutralized Sodium percarbonate 10.5 10.5 10.5 TAED 4 4 4 Na₂Si₂O₅ 2 2 2 Na₂CO3 19.5 19.5 19.5 Sodium citrate dihydrate 15 22.5 30 HEDP 0.5 0.5 0.5 ethoxylated polyethylenimine, 20 optionally: optionally: optionally: EO/NH group, M_(n): 30,000 g/mol 0.1 0.1 0.1

Laundry detergent compositions according to the invention are useful for laundering any type of laundry, and any type of fibres. Fibres can be of natural or synthetic origin, or they can be mixtures of natural and synthetic fibres. Examples of fibers of natural origin are cotton and wool. Examples for fibers of synthetic origin are polyurethane fibers such as Spandex® or Lycra®, polyester fibers, or polyamide fibers. Fibers may be single fibers or parts of textiles such as knitwear, wovens, or nonwovens.

The invention is further illustrated by working examples.

General Remarks:

The ee value was determined by HPLC using as column Chirex 3126; (D)-penicillamine, 5 μm, 250·4.6 mm. The mobile phase (eluent) was 0.5 mM aqueous CuSO₄-solution. Injection: 10 μl, flow: 1.5 ml/min. Detection by UV light at 254 nm. Temperature: 20° C. Running time is 20 min. The ee value of (A) was determined as difference of the area-% of the L- and D-MGDA peak. Sample preparation: A 5 ml measuring flask was charged with 5 mg of test material and then filled mark with the eluent and then homogenized.

In each case, the solubility was calculated to refer to pure MGDA, without hydrate water.

I. Syntheses of Inventive Mixtures

With exception of ee values, percentages in the context of the examples refer to percent by weight unless expressly indicated otherwise.

I.1 Synthesis of a Solution of Partially Neutralized D,L-alanine bis-acetonitrile (ABAN) Containing L-aspa-bis-acetonitrile (Asp-BAN), Steps (a.1) and (b.1)

Step (a.1): A 1-litre stirred flask was charged at room temperature with 265.4 g of de-ionized water. Amounts of 133.7 g of D,L-alanine (1.5 mole) and 0.33 g (2.5 mmol) L-aspartic acid were added. To the resultant slurry 78.0 g of 50% by weight aqueous sodium hydroxide solution (0.98 mole) were added. After complete addition of the sodium hydroxide the slurry was stirred at 50° C. for 30 minutes. A clear solution was obtained.

Step (b.1): A 1.5-litre stirred flask was charged with 125 ml of de-ionized water at room temperature. Then, 477 g of the solution according to step (a.1), 309.0 g of 30% by weight aqueous formaldehyde solution (3.09 mole) and 66.4 g of hydrogen cyanide (99.4%, 2.44 mole) were added simultaneously at 40° C. within 30 minutes. The resulting solution was then simultaneously added to a 1.5-litre flask (containing additional 125 ml of de-ionized water) together with additional 16.7 g of hydrogen cyanide (99.4%, 0.62 mole) at 40° C. within 30 minutes. Upon completion of the addition the reaction mixture was stirred for additional 60 minutes at 40° C. A solution was obtained that contained partially neutralized D,L-alanine bis-acetonitrile (ABAN) and L-aspartic acid bis-acetonitrile.

I.2 Synthesis of an Aqueous Solution of MGDA-Na3 and Aspartic Acid-N,N-Diacetic Acid TetraSodium Salt, ASDA-Na4, Steps (c.1) and (c.2)

Step (c.1): A 1.5-litre stirred flask was charged with 121 ml of de-ionized water and 29 g of 50% by weight aqueous sodium hydroxide solution and heated to 45° C. Then, simultaneously 1.125 g of the solution prepared according to step (b.1) and 259.0 g of a 50% by weight aqueous sodium hydroxide solution were added dropwise within 60 minutes. An exothermic reaction could be observed. The reaction mixture was stirred for 60 minutes at 60° C.

Step (c.2): The reaction mixture obtained according to (c.1) was stirred at 94 to 95° C. for 5 hours. The color of the reaction mixture turned to light orange. The NH₃ formed during the reaction was continuously removed by stripping. The volume of the reaction mixture was kept constant by repeated addition of water.

A 40% by weight solution of D/L-MGDA-Na₃nd ASDA-Na₄ was obtained. The overall yield was 95%, determined by titration of Fe(III+) in the form of FeCl3 in aqueous solution.

2. Testing of Stability of Solution

50 ml of an aqueous solution according to 1.2 were concentrated to 45% solids content and then stirred at 23° C. over a period of time of 5 days. No precipitate formation could be observed.

10 ml of an aqueous solution according to 1.2 were placed in a petri dish and left under the following conditions for 48 hours: 50° C., 60% relative humidity. After this period of time, aqueous solution according to 1.2 was still a clear solution.

For comparison purposes, MGDA-Na₃ was synthesized by reacting acetaldehyde and hydrocyanic acid with iminodiacetonitrile, HN(CH₂CN)₂, in a molar ratio of 1:1:1 followed by subsequent saponification of the nitrile groups with a stoichiometric amount of NaOH as aqueous sodium hydroxide solution. The NH₃ formed during the reaction was continuously removed by stripping. The volume of the reaction mixture was kept constant by repeated addition of water. A 40% by weight aqueous solution of racemic MGDA-Na₃ was obtained. Said solution was concentrated to 45% by weight and then stirred at 23° C. over a period of time of 5 days. A significant turbidity could be observed.

10 ml of the above comparative solution were placed in a petri dish and left under the following conditions for 48 hours: 50° C., 60% relative humidity. After this period of time, significant precipitation could be observed. 

The invention claimed is:
 1. A mixture, comprising: (A) 90 to 99.999% by weight of racemic methyl glycine diacetic acid (MGDA) or of MGDA with predominantly the L-isomer in an enantiomeric excess of up to 9.5% or their respective mono-, di- or trialkali metal or mono-, di- or triammonium salts; and (B) 0.001 to 10% by weight of the diacetic acid derivative of aspartate as free acid or as mono-, di-, tri- or tetraalkali metal salt or as mono-, di-, tri- or tetraammonium salt, percentages referring to the sum from (A) and (B).
 2. The mixture according to claim 1, wherein (A) is selected from the group consisting of racemic MGDA and the mono-, di- and trisodium salts of racemic MGDA.
 3. The mixture according to claim 1, wherein the component (B) is predominantly the L-isomer with an enantiomeric excess (ee) in the range of from 10 to 95%.
 4. The mixture of claim 1, comprising: (A) 95 to 99.99% by weight of the racemic methyl glycine diacetic acid (MGDA) or of the MGDA with predominantly the L-isomer in an enantiomeric excess of up to 9.5% or their respective mono-, di- or trialkali metal or mono-, di- or triammonium salts; and (B) 0.01 to 5% by weight of the diacetic acid derivative of aspartate as free acid or as mono-, di-, tri- or tetraalkali metal salt or as mono-, di-, tri- or tetraammonium salt.
 5. The mixture of claim 1, further comprising from 0.1 to 10% by weight of one or more optically inactive impurities, at least one of the impurities being selected from the group consisting of iminodiacetic acid, formic acid, glycolic acid, propionic acid, acetic acid and their respective alkali metal or ammonium salts.
 6. The mixture of claim 1, further comprising 0.01 to 5% by weight, referring to the sum of (A) and (B), of glutamic acid diatetic acid (GLDA) or its respective mono-, di-, tri- or or tetraalkali metal or mono-, di-, tri- or tetraammonium salt.
 7. An aqueous solution, comprising from 45 to 70% by weight of a mixture according to claim
 1. 8. A process for making the mixture of claim 1, the process comprising: (a) dissolving a mixture of alanine and aspartate in water or an aqueous solution of an alkali metal hydroxide; (b) converting the respective dissolved amino acids and their respective alkali metal salts with formaldehyde and hydrocyanic acid or alkali metal cyanide to the respective dinitriles; and (c) saponification of the dinitriles resulting from step (b), employing stoichiometric amounts of hydroxide or an excess of 1.01 to 1.5 moles of hydroxide per molar sum of COOH groups and nitrile groups of the dinitrile from step (b).
 9. The process according to claim 8, wherein step (c1) is carried out at a temperature in the range of from 20 to 80° C. and step (c2) is carried out at a temperature in the range of from 75 to 200° C.
 10. A laundry detergent composition, comprising the aqueous solution according to claim
 7. 11. A process, comprising fully or partially neutralizing the aqueous solution according to claim 7 to obtain a laundry detergent composition, wherein the neutralization is performed with an inorganic acid.
 12. A process, comprising fully or partially neutralizing the aqueous solution according to claim 7 to obtain a laundry detergent composition, wherein the neutralization is performed with an organic acid. 